This invention relates to a passenger conveyor system, and more particularly to a safety system including a communication bus that connects safety related components.
A typical passenger conveyor, such as an escalator or moving walk, includes a truss, a plurality of sequentially connected treadplates traveling through a closed loop path within the truss, and a machine for driving the treadplates.
Escalators and moving walks include devices such as sensors for monitoring speed, sensors for detecting missing treadplates, devices for monitoring wear; actuators for utilizing special purpose devices and output devices, such as traffic lights. Each of these devices includes a combination of interface devices, i.e., sensors, switches or actuators, that are connected to a central control. To assure the continued operation of the sensors typical passenger conveyers include a safety system that monitors and responds to each sensor.
Conventional escalator safety systems are implemented using a Safety Chain which is a serial circuit of the switches and contacts. The Safety Chain operates relays (or contactors) that handle the power to the escalator motor. An operation of any contact within the chain will disconnect the motor or drive from the main power supply. The serial connections of the contacts and the bridging for inspection leads to a long chain which requires higher voltages to minimize the effects of voltage losses along the chain.
Because the Safety Chain is wired in serial, a failure cannot be specifically identified. During maintenance and inspection, it is sometimes necessary to include bridges in the Safety Chain by hand for testing and error searching. Manual installation and removal of the bridges is time consuming and labor intensive. Further, the serial connection renders remote checking difficult.
Therefore it has been determined that a need exists for an improved safety system which lowers part count and manufacturing costs, all while improving operability.